Centering mechanism for the shovel of shovel loaders



April 27, 1954 F, B, ENGEL 2,676,717

CENTERING MECHANISM FOR 4THE sHovEL oF sHovEr. LoADERs original Fild may 22, 194e L ,g IIA? willful@ LiL/ d m @0:76

I s sheets-sheet 1 Y F. B. ENGEL April 27, 19514 676,717 CENTERING MECHANISM FOR THE sHovEL oF sHovEL. LoADERs original Filed May 22, 194e :s sheeisshee'i- 2 11H.. Ilu. Il

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April 27, 1954 F. B. ENGEL 2,676,717

CENTERING MECHANISM FOR THE SHOVEL OF SHOVEL LOADERS oEZzgeZ. M

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Patented Apr. 27, 1954 CENTERING MECHANISM FOR THE SHOVEL OF SHQVEL LOADERS Fiesco B. Engel, Claremont, N. H., assignor to Joy Manufacturing Company, Pittsburgh, Pa., a corporation of Pennsylvania Continuation of application Serial No. 671,528, May 22, 1946. This application November 18, 1952, Serial No. 321,233

7 Claims. (Cl. 214-132) This invention relates to material loading apparatus and more particularly to an improved. shovel loader having improved means for automatically centering the shovel with respect to the loader base as the shovel swings upwardly from a laterally located digging position toward its raised dumping position.

In material loading apparatus of the type known as a shovel loader, the shovel is usually mounted on a turntable on a portable base to swing laterally into digging positions at either side of said base, and the shovel is swingable in a vertical direction relative to said turntable between its lowered digging position and its raised dumping position. The shovel is usually swung manually horizontally on its turntable mounting to locate the shovel in the desired digging positionv at the side of the base, and the shovel after it has been swung upwardly a predetermined relatively `short distance sulicient-to clear the pile of material to be loaded, is automatically aligned with the base as the shovel continues to be swung upwardly and rearwardly toward its,

raised dumping position so that discharge of the shovel contents into a mine car, located rearwardly of the loader base, is assured. In certain known types of automatic self-centering means, such as those actuated or controlled by the shovel raising means, it is not possible to swing manually the shovel horizontally into a lateral position until it approaches its lowered position,

and, accordingly, the operator must wait-- until the shovel is nearly lowered before he can manually swing the shovel to one side. Thus such substantial delay in the lateral swinging of the shovel greatly increases the overall loading time.

The present invention, ina preferred embodiment, contemplates an improvement over the automatic centering means of the type above outlined in that the automatic centering means is: always automatically rendered inactive as soon as the shovel has moved forwardly a relatively' short distance from its raised dumping position so that as the shovel swings forwardly and downwardly, the operator can manually horizontally swing the shovel on its turntable mounting into the desired lateral digging position with respect to the loader base. Thus, in a preferred embodiment of the invention, when the shovel is in a laterally located digging position withy respect to the loader base, it starts automatically to center after the shovel has moved upwardly a predetermined vrelatively short distance so that as the shovel continues to travel through a substantial portion of itsupward path, itis in alignmentrwith;

shovel raising means.

the loader base; and, conversely, as the shovel starts toyreturn from its raised dumping position, the automatic centering means is automatically rendered inactive so that the shovel can be turned manually horizontally to one side as it continues to move downwardly toward its lowered digging position, thereby increasing the overall loadingV speed of the loader. o

An object of the present invention is to provide an improved material loading apparatus.

Another object is to provide an improved shovel Y loader having improved automatic centering Y means for the shovel, embodying advantages over certain known types of devices. Another object is to provide an improved shovel loader having improved means for automatically centering the shovel after it has moved upwardly a predetermined relatively short distance sufficient to clear the pile of material to be loaded and, conversely, which is automatically rendered inactive after the shovel has moved forwardly a corresponding predeterminedl relatively short distance from its raised dumping position. Still another object is to provide an improved shovel loader having im- ;-proved means for automatically aligning the Y shovel relative to the loader base after the shovel has moved upwardly a predetermined relatively short distance from its lowered digging position and which is controlled by an element of the provideV an improved automatic centering means of the iiuid operated type forautomatically centering the shovel of a shovel loader as the shovel moves upwardly a relatively short distance from :its lateral digging position and embodying improved control means for venting the iiuid in the centering means after the shovel has moved forwardly a corresponding relatively short distance from its raisedrdumping position. Yet another .object is to provide an improved automatic valve means for controlling the supply of operating uid to the automaticshovel centering means and embodyingimproved means driven by an element of the shovel raising means for automatically controlling the valve means. Other objects and advantages of the invention will, however, hereinafter more fully appear in the course ofthe following description.

This application is a continuation of my application Serial No. 671,528, filed May 22, 1946, and

now abandoned.

In the accompanying drawings there are shown for purposes of illustration one form and two modifications which the invention may assume in practice. l f y A still further object is to In these drawings:

Fig. 1 is a side elevational view of a shovel loader in which a preferred illustrative embodiment of the invention is incorporated, with different vertical loading positions of the shovel shown in dotted lines.

Fig. 2 is a plan view of the shovel loader shown in Fig. 1, with the lateral digging positions of the shovel shown in dotted lines.

Fig. 3 is an enlarged horizontal sectional view taken substantially on line 3 3 of Fig. 1.

Fig. 4 is a view in longitudinal vertical section taken substantially on line 4-4 of Fig. 3.

Fig. 5 is a cross-sectional view taken substantially on line 5-5 of Fig. 3.

Fig. 6 is a detail vertical sectional view taken on line 6 6 of Fig. 3.

Fig. 7 is a detail view in longitudinal vertical section taken substantially on line 'L-I of Fig. 3.

Fig. 8 is an enlarged cross-sectional view taken substantially online 8-3 of Fig. l, looking toward the rear end of the loader.

Fig. 9 is an enlarged detail vertical sectional view, with parts in elevation, taken on line 9-9 of Fig. 8.

Fig. 10 is a detail vertical sectional view taken substantially on line I--Ili -of Fig. 9.

Fig. ll is a horizontal sectional View taken on line II-II of Fig. 9.

Fig. 12 is a detail vertical sectional view taken on the plane of Fig. 9, showing the moving parts in a different position.

Fig. 13 is a vertical sectional view illustrating a modiiied form of the invention.

Fig. le is a vertical sectional view showing still another modified form of the invention.

Fig. 15 is a diagrammatic view showing the fluid system and its associated control means.

In the preferred illustrative embodiment of the invention there is shown a shovel loader, generally designated I, which may be "of the same general character as that disclosed in a patent to R. C. Osgood, No. 2,268,569, patented January 6, 1942, and the shovel loader, as embodied herein, embodies improved automatic shovel centering means, generally designated 2, which constitutes an improvement over that of the patent. Evidently, the invention may be lembodied in loading apparatus of other types.

The shovel loader herein comprises a portable base 3 having a base frame 4 mounted on wheels 5 adapted to travel along a trackway 6. Swivelled on the base is a horizontal turntable 1 on which a vertically swingable shovel or bucket 8 is mounted. The base frame 4 has xed thereto a vertical shaft 9 (Figs. 3 and 5) supporting bearings on which the turntable is journaled, and the turntable may be turned on its bearing mounting into positions to locate the shovel laterally at either side of the base,'as indicated in dotted lines in Fig. 2, so that the shovel may vdig into the material to be loaded at either side'of the trackway. As disclosed in the patent above referred to, a conventional reversible uid motor I0 on the base frame 4 beneath the turntable is operatively connected to the wheels 5 for propelling the loader back and forth along the trackway, and the traction of the wheels is utilized to effect digging of 'the shovel forwardly into the material to be loaded. Coupled to the rear end of the loader base is a mine car M, having its wheels guided on the trackway.

As is also fully described inthe above mentioned patent, the shovel or bucket Bissnpported by arms II, which carry rolls I2 guided in substantially horizontal guideways I3 on the inner sides of the vertical side plates I4 on the turntable. Thus the rollers provide a rolling pivotal support for the shovel and the shovel supporting arms are swingably supported to turn on axes coincident with the roll support axes as the shovel is swung about its iulcrum point, and as the shovel is swung upwardly from its lowered digging position, the rollers move rearwardly lalong the guideways and the guideways serve to confine the shovel as it swings upwardly to move in a predetermined lcurved path. Secured to the arms `are segments :I5 of semi-circular shape (see Fig. l) having cable guiding grooves for receiving pairs of .flexible spring-tensioned cables I6, |15r and I1, I1, each `of which is secured at one end to the yshovel arms and at its other end to the turntable frame. These pairs of cables serve to compel swinging movement of the arms, thereby to effect movement of the shovel side arms bodily longitudinally as they are swung, and vto provide, in effect, a moving fulcrum point for the shovel; and they serve to effect movement of the shovel through a wide arc as it moves between its lowered digging position and its raised dumping position. The arm segments, roller mounting and cable connections are fully described in the patent above referred to.

For raising and lowering the shovel on its roller mounting, there are provided side chains I8 fastened to the shovel arms and wound on drums I3 (Fig. 8) xed to a transverse shaft 20 suitably journaled in bearings supported by the vertical side plates I4. A conventional reversible fluid motor 2| is mounted on the'turntable and has its power shaft connected through a chain and sprocket drive 22 to the drum shaft 20. The motor has a conventional reversing valve 23 operated by a hand lever 24. This structure is also fully described `Vin the patent abovev referred to.

Pressure ,fluid `may be supplied to the motors II) and 2I through a supply hose 25 on the base coupled to branched pipe connections 23 and 2l (Figs. 1 and 5) arranged on the base frame beneath the turntable. The pipe connection 2l is connected to the lower end of an axial passage 28 in the stationary vertical shaft 9 (Figs. 3 and 5) and the upper end of the passage 23 is connected by a flexible hose 29 to the iiuid supply for the shovel motor 2l. Carried by a cross plate 3@ which braces the vertical side plates I4, are spring buiers 3|, 31 engageable by the shovel supporting arms II to provide a cushioned stop for the shovel when the latter assumes its raised dumping position as indicated in dotted lines at the extreme right in Fig. 1. When the rearward movement of the shovel is abruptly stopped by the buffer springs",` the shovel contents are discharged into themine Acar M. The buiier springs also initiate forward movement of the shovel from its raised dumping` position and when the center of .gravity is passed, the shovel will drop down to its digging position under its own weight. To speed up the return of the shovel, the shovel .motor 2l is reversed to rotate the cable drums I9 in unwinding direction to slacken the side chains I8 so that the shovel may freely drop down into its digging position. This structure, also, is described in the above mentioned patent.

The automatic centering mechanism 2 serves to align the shovel` with respect to the loader base as the shovel moves upwardly from a laterally located digging position so that discharge of the shovel contents into the 'mine car M is ,Y tending longitudinally along one side of the base frame beneath the turntable and containing oppositely acting reciprocable pistons 36, 36. These pistons are pivotally connected by links 31 to horizontally swingable arms 38, 38 -pivoted on vertical pivot pins 39 secured to the top ofthe base frame. These arms are swingable horizontally into engagement with a roller 40 (Fig. 4) journaled on the lower end of a vertical pin 4| secured to the swivelled turntable 1. "Ihispin projects vertically through an arcuate slot -42 struck on a radius fromthe'turntable axis in thel top of the base frame. The pin 4| and roller 46 are movable horizontally with the turntable relative to the base frame and the arcuate slot in the top of the base frame permits such move` ment. Pressure iluid may be supplied 'to'the centering cylinders 35 at the remote ends of thel pistons through hoses 43, 43 connected to passages 44 in the outer cylinder head and connected at their adjacent ends by a T 45 to a hose 46, the latter having communication with an axial pasage 41 (Figs. 3 and 5) in the shaft 9. The passage 41 has fluid supplied thereto as .will later be described. It will thus be seen that pressure fluid may flow from the passage 41 in the shaft 9, through hose 46, T 45, hoses 43, 43 and the passages 44 in the cylinder heads, con` currently to the remote ends of the cylinder bores. Arranged on the base frame beneath thev turntable is a vertically disposed 'uid cylinder 49 (Figs. 3 and 7) containing a reciprocable piston 50 having its piston rod 5| extending upwardly within the top cylinder head, and the upper end of this piston rod has formed thereon a locking pin 52 which is receivable in a lockingrece'ss 53 formed in the turntable 1. A coil spring 54 urges the piston downwardly toward its released position. A hose 55 communicates with the lower end of the cylinder 49 for supplying pressure c; fluid to the cylinder, and this hose is connected to one of the hoses 43 so that when pressure uid is supplied to the centering cylinders 35, 35, it is supplied concurrently to the locking cylinder 49. It will thus .be seen that when the shovel supporting turntable is power-swung from a' lateral position into alignment with the loader base, it is automatically locked in such position by the locking pin 52. When the centering cylinders are vented to atmosphere, the locking cylinder 49 is concurrently vented.

Now referring to the improved automatic control means, generally designated 56, actuated 'This centering mechanism 'may be by the shovel raising motor for controlling the supply of pressure uid to 'and the venting 4of fluid from the centering and locking cylinlders, it will be noted that mounted on a bracket 51 secured to the cross plate 30 is a valve casing 58 having a horizontal bore 59 (Fig. 11) containing a slide valve 60. The valve has spaced spools 6| connected by a reduced portion 62 and has a valve stem 53 extending outwardly through an outer head 64 of the valve casing. A coil spring 65 constantly urges the valve toward the rightas viewed in Fig. 11. The valve stem is engageable by an arm of a lever 66 pivoted atv 61 on the bracket 51. The other arm of the lever is engageable by an actuator 69 preferably slidably mounted von the drum shaft 20. This actuator is-secured to a rotatable nut 10 having a cylindrical body guided in a bore 1| in a guide frame smooth exterior periphery of the cylindrical nut l 10, frictionally to hold the latter against rotation until its axial movement along the shaft 20 is limited either by the collar 15 or the valve actuating lever 66 and the valve; and when axial movement of the nut is prevented, the shoe slips to permit rotation of the nut with the screw. A spring 11 is adjustable by a screw plug 18. A hose 19 connects a passage 80 communicating with the valve-receiving bore 59 to the supply hose 29 and a hose 8| communicating with the valve-'receiving bore is connected to the upper end of the passage 41 in the shank 9 (Fig .5). The valve-receiving bore is connected to atmosphere by a vent port 82.

When the shovel 8 vis in either of its laterally located digging positions shown in dotted lines in Fig. 2 and the motor 2| is operated to raise the shovel from its lowered digging position as indicated in full lines at A in Fig. 1, the drum shaft 20 rotates in a direction to wind in the side chains 8 and concurrently to cause the screw 14 to move the nut 10 toward the right as viewed in Figs. 9 and 12, moving the actuator 69 to swing the lever 66 to shift the valve 66 toward the left as viewed in Fig. 11, thereby to admit pressure uid from the supply hose 2,9 and hose 19 past the valve to the hose 8| connected to the passage 41 in the shaft 9 and thence through hoses 46 and 43 to the centering cylinders 35 and through hose to the locking cylinder 49. The pitch of the screwthreads is such that the shovel may move upwardly a predetermined relatively short distance sufficiently to clear the pile of material to be loaded as indicated in dotted lines swings upwardly and rearwardly toward its raised dumping position indicated in dotted lines at C in Fig. 1, the shovel is aligned with the loader base; and when the shovel approaches its dumping position, the shovel side arms engage the buffer springs 3| so that the shovel is abruptly f stopped and the shovel contents are discharged into the mine car M. When the shovel is in its raised dumping position, the motor 2| is reversed by the reversing valve 23 to effect slackening of the side chains I8 and the 'buffer springs bounce the shovel forwardly past its center of gravity, and when the shovel moves forwardly to the dotted line position indicated at D in Fig. 1, the drum shaft 20 is rotated suiiciently in the reverse 1 direction to cause the screw to move the nut toward the left as viewed in Figs. 9 and l2 to permit movement of the valve under the influence of the 'spring 65 to the position shown in Fig. l,

' therebyto connect the pipe 8| to the vent 82 to vent the centering and locking cylinders to render the automatic centering means inactive.

Thus, when the shovel is moved forwardly a corresponding predetermined relatively short distance from its raised dumping position, the automatic centering means is rendered inactive so that the operator can manually horizontally swing the shovel on its turntable mounting into the desired lateral digging position with respect to the loader base as the shovel continues to move downwardly toward its lowered digging position. By enabling manual turning of the shovel as the shovel swings downwardly toward its digging position, the overall loading speed ci the loader is substantially increased.

In the modiiication shown in Fig. 13", the control valve 6i). is operated by a lever arm 85 secured to one of a pair of cooperating hinged shoes 8B and itl lined with friction material and yieldingly held in frictional engagement with the drum shaft 29 by a coil spring 88 engaging a bolt 89 connected between the arm and the free end of the shoe Sl. When the drum shaft 20 rotates in a direction to effect raising of the shovel, the friction shoes tend to rotate with the shaft, causing the le-ver arm 85 to move toward the left as viewed in Fig. 13 to engage the valve stem to shift the valve to effect fluid supply to the centering and locking cylinders. When the drum shaft 20 is driven in the reverse direction during lowering of the shovel, the friction shoes cause the lever arm to move toward the right to permit movement of the valve into its position wherein the centering and locking cylinders are vented. The arrangement of the shoes and lever arm with respect to the valve is such that there is a slight delay prior to operation of the centering cylinders sufficient to permit the shovel to raise a predetermined relatively short distance to clear the pilev of material to be loaded before automatic centering occurs, and, conversely, when the shovel starts to move forwardly and downwardly a corresponding predetermined relatively short distance from its' raised dumping position, the shoes and lever arm cause the valve to be moved quickly into its venting position thereby to render the automaticcentering means inactive.

The modification shown in Fig. le is similar to that shown in Fig` l2. In this construction the drum shaft 20 is connected by a chain and sprocket drive 9| to a parallel shaft 92 journaled in a bracket 93 which may be secured to the cross plate 3i). Formed on the shaft 92 is a screw 14: threadedly engaging a nut 1B". The control valve, in this instance, is aligned with the screw and nut so that the nut directly engages the valve stem. As in the preferred embodiment, when the drum shaft 20 is rotated in shovel raising direction, the nut it' is moved by the screw toward the right in Fig. i4 to movethe control valve into its huid supply eecting position thereby to effect operation of the automatic centering means. When the drum shaft 20 is reversed during lowering of the shovel', the screw is reversed, causing the nut to move toward the left to permit movement of the valve into its venting position to render the automatic centering means inactive. Otherwise, the mode of operation of this modined construction is similar to that of the preferred embodiment.

It is accordingly evident that the automatic control means for the centering valve permits the shovel to be raised a predetermined relatively short distance to clear the pile of material being loaded without centering, and after the shovel has been raised suniciently to clear the pile of* material, centering automatically occurs so that discharge of the shovel contents into the mine car M is assured. Also when the shovel moves forwardly a corresponding predetermined relatively short distance from its raised dumping position, the control valve is actuated by the improved control means to effect venting so that the automatic centering means is rendered inactive, thereby enabling the operator manually to turn theA shovel into the desired lateral digging position with respect to the loader base as the shovel swings downwardly. As the general mode of operation of the shovel loader of the type disclosed is well known to those skilled in the art and'is fully described in the patents above referred to, further description thereof herein is unnecessary. Other uses and advantages of the invention will be clearly apparent to those skilled in the art.

While there are in this application speciiically described one form and two modications which the invention may assume in practice, it will be understood that these forms and modiiications of the same are shown for purposes of illustration and that the invention may be further modified and embodied in various other forms without departing from its spirit or the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent is:

l. In a. controlling mechanism for a shovel loader of the type comprising a portable base, a frame swivelled on said base to turn relative thereto about a vertical axis, a shovel pivotally mounted on said swivelled frame to swing in a vertical direction relative thereto between a lowered digging position and a raised dumping position, means for swinging said shovel in a vertical direction relative to said frame including a rotatable swing-effecting member operatively connected to said shovel and a rotatable driving element for said rotatable member and power operated means for turning said frame horizontally about its vertical axis relative to said base,

3 'thc vcombination comprising means actuated by said driving element for automatically controlling said turning means upon movement of said shovel a predetermined relatively short distance from its lowered digging position to effect operation of said turning means to turn said frame and for rendering said turning means inactive upon movementy of said shovel in the opposite direction a corresponding predetermined relatively short distance from its lraised. dumping position, said controlling means including a rotatable controlling member, means for effecting movement of said controlling member bodily a limited distance relative to said rotatable member and to interrupt such bodily movement, and rictional means for holding said controlling member against rotation during such bodily movement thereofv and slipping automatically to provide for rotation of said controlling member upon interruption of bodily movement thereof after said controlling member has travelled such limited distance.

2. Ina controlling mechanism for a shovel loader of the type comprising a portable base, a shovel mounted on said base to swing horizontally relative thereto into a laterally located material receiving position at one side of said base. means for moving said shovel upwardly in a vertical direction relative toy said base ybetween its material receiving position and its material disx. charging position and for permitting downward `movement of said shovel toward material receiving position, said shovel moving means including a rotatable driving element, and power operated self-'centering means for said shovel for aligning the latter with said base irrespective of the horizontally swung position of said shovel relative to said base, the combination comprising means embodying a shiftable control element actuated by said driving element of said shovel moving means for automatically controlling the flow of power medium with respect to said centering means, said control element movable into one position for automatically effecting operation of said centering means shortly after initiation of movement of said shovel upwardly in a vertical direction from its material receiving position and movable into a diierent position for automatically rendering said centering means inactive shortly after initiation of movement of said shovel from its material discharging position downwardly toward its material receiving position, said automatic controlling means also including a rotatable driving element, and frictional means for holding said control element against rotation with said last mentioned driving element during its actuation by said latter driving element into either of its operating positions, and said frictional means providing for rotation of said control element with said latter driving element when either of said operating positions is reached.

3. In a controlling mechanism for a shovel loader of the type comprising a, portable base, a frame swivelled on said base to turn relative thereto about a vertical axis, a shovel pivotally mounted on said swivelled frame to swing in a vertical direction relative thereto between a lowered digging position and a raised dumping position, means for swinging said shovel upwardly in a vertical direction relative to said frame and for permitting lowering of said shovel, said swinging means including a rotatable member operatively connected to said shovel and a driving element for said rotatable member and power operated means for turning said frame horizontally about its vertical axis relative to said base, the combination comprising means embodying a shiftable control element for regulating the iiow of power medium to said turning means and for interrupting such ilow, said control element actuated by said driving element for automatically controlling said turning means and movable into one position upon movement of said shovel a predetermined relatively short distance upwardly from its lowered digging position to effect operation of said turning means to turn said frame and movable into a diierent position for rendering said turning means inactive upon movement of said shovel in the opposite direction a corresponding predetermined relatively short distance from its raised dumping position, said automatic controlling means also embodying a drive member for actuating said control element for shifting the latter relative to said drive member into either of said operating positions and means for limiting such movement of said control element in either direction and providing for movement of said control elevment in unison with said drive member when either of said positions is reached.

4. In a controlling mechanism for a shovel loader of the type comprising a portable base, material loading means supported on said base including a shovel movable upwardly and downwardly between material receiving and discharg- -10 ing positions, means for effecting movement oi said shovel between said positions including a reversible rotatable driving element, means includingv a mounting swingable about a vertical pivot for enabling the positioning of said shovel laterally out of central relation to said base into digging positions at either side of said base and power operable means for applying a centering force to eect movement of said shovel about said vertical pivot from a lateral digging posi- `tion to a central position with respect to said base; the combination comprising controlling means for said power operable means automatically governed by shovel movement upwardly and downwardly and movable into one position for causing said power operable means to apply a centering force to said shovel upon the completion of a predetermined relatively small portion of the upward movement' of the latter and movable into a different position to effect release of said shovel from the centering force applying action of said power operable means upon the completion of a correspondingly relatively small portion of the downward movement of said shovel, said automatic controlling means including a movable control member for regulating the flow of power medium to said centering force applying means and actuating mechanism for said control member including a shiftable element driven by a reversible element of said shovel movement effecting means and moving in one direction as said shovel moves upwardly and moving in the opposite direction as said shovel moves downwardly depending upon the direction of operation of said reversible driving element, means for limiting the travel of said shiftable element in either direction, and means providing for movement of said reversible element relative to said shiftable element when the movement of the latter is limited by said limiting means.

5. A controlling mechanism as set forth in claim 4 wherein said movement providing means comprises a frictional device through which said shiftable element is driven by said reversible driving element until the movement of said shiftable element is interrupted by said limiting means.

6. A controlling mechanism as set forth in claim 5 wherein said shirtable element moves for a short distance during the initial movement of said reversible driving element in either direction of movement of the latter so that when said shovel has moved either upwardly or downwardly substantially its distance of movement, said shiftable element is actuated into positions to eect control of said movable control member.

7. In a controlling mechanism for a shovel loader of the type comprising a portable base, material loading means SuDpQrted on said base including a shovel movable upwardly and downwardly between material receiving and discharging positions, means for eiecting movement of said shovel between such positions including a reversible rotatable drive shaft and an element driven thereby, means including a mounting swingable about a vertical pivot for enabling the positioning of the shovel laterally out of central relation to said base and power operable means for app-lying a centering force to eiect movement of said shovel about said vertical pivot to a central position with respect to said base, the combination comprising automatic controlling means for said power operable means governed by shovel movement upwardly and downwardly and including shiftable control means for regulating the ow 11 of power medium to said power operable means and for interrupting such flow, said control means actuated by said element of said shovel-movement-effecting means and movable into one position for causing said power operable means to apply a centering force to the shovel upon the completion of a predetermined relatively small portion of the upward movement of the latter and movable into a different position to effect release of the shovel from the centering force applying action of said power operated means upon the completion of a corresponding relatively small portion of the downward movement of the shovel, said shiftable control means comprising a control element frictionally mounted on said shaft, stop means for limiting movement of said control element with said shaft to a partial rotation in either direction of movement of said shaft,

and a Vcontrol member for said power operable means actuated in one direction by said vcontrol element as the latter is partially rotated by said shaft in one direction, said control element upon movement of said shaft in the opposite direction being effective to permit movement of said control member in the opposite direction.

References Cited-in the le of this patent UNITED STATES PATENTS 

